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Highly tunable perpendicularly magnetized synthetic antiferromagnets for biotechnology applications.

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Vemulkar, T 
Petit, DCMC 
Cowburn, RP 
Lesniak, MS 


Magnetic micro and nanoparticles are increasingly used in biotechnological applications due to the ability to control their behavior through an externally applied field. We demonstrate the fabrication of particles made from ultrathin perpendicularly magnetized CoFeB/Pt layers with antiferromagnetic interlayer coupling. The particles are characterized by zero moment at remanence, low susceptibility at low fields, and a large saturated moment created by the stacking of the basic coupled bilayer motif. We demonstrate the transfer of magnetic properties from thin films to lithographically defined 2 μm particles which have been lifted off into solution. We simulate the minimum energy state of a synthetic antiferromagnetic bilayer system that is free to rotate in an applied field and show that the low field susceptibility of the system is equal to the magnetic hard axis followed by a sharp switch to full magnetization as the field is increased. This agrees with the experimental results and explains the behaviour of the particles in solution.



Magnetic susceptibilities, Antiferromagnetism, Magnetic films, Magnetic hysteresis, Magnetic anisotropy

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Appl Phys Lett

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AIP Publishing
Engineering and Physical Sciences Research Council (EP/G037221/1)
European Research Council (247368)
This research is funded by the European Community under the Seventh Framework Program ERC Contract No. 247368: 3SPIN, NIH grant R01NS077388 "Magnetic Vortex Microdiscs for Glioma Therapy" and the EPSRC Cambridge NanoDTC, EP/G037221/1.